In AD 449, between the third and fourth Councils, another council was held in which St. Cyril's successor, Dioscorus of Alexandria, "insisted that there is in Christ only one nature (physis)". It is a position commonly called Monophysite, and it states that the Savior "is from two natures, but after His Incarnation there is only 'one incarnate nature of God the Word'." St. Cyril himself had used those words, but Dioscorus omitted many of the balancing statements that St. Cyril had made. And so, only two years later, Emperor Marcian called a new gathering of Bishops to decide the matter. This gathering, in AD 451 is what is considered the fourth great Council.

Concerning Christ's nature and personhood, the Council rejected Dioscorus' position, and proclaimed that:

...while Christ is a single, undivided person, He is not only from two natures but in two natures. The bishops acclaimed the Tome of St. Leo the Great, Pope of Rome (died 461), in which the distinction between the two natures is clearly stated, although the unity of Christ's person is also emphasized. In their proclamation of faith they stated their belief in 'one and the same son, perfect in Godhead and perfect in humanity, truly God and truly human... acknowledged in two natures unconfusedly, unchangeably, indivisibly, inseparably; the difference between the natures is in no way removed because of the union, but rather the peculiar property of each nature is preserved, and both combine in one person and in on hypostasis.

This definition, where the distinction between Christ's two natures and the unity of His personhood are both emphasized, was aimed not only at the Monophysites, but also the followers of Nestorius.

Concerning the visible organization of the Church, Canon 28 confirmed Canon 3 of the Second Council and left the assignment of Constantinople, or New Rome, second in honor after 'old' Rome. This was a blow to the Alexandrians and their desire to "rule supreme" in the east. Leo of Rome rejected this canon, but the east has always recognized its validity. The Council also freed Jerusalem from the jurisdiction of Ceasarea and gave it fifth place among honor, thus creating what is know by the Orthodox as the 'Pentarchy'. This Pentarchy settled the order of precedence. In order of rank:

Rome

Constantinople

Alexandria

Antioch

Jerusalem

All five sees claimed Apostolic foundation. The first four were the most important cities in the empire, and Jerusalem was added because it is where Christ suffered and rose from the dead. Also, it was during this council that the bishops in each city received the title "Patriarch." The Patriarchates then divided the whole of the known world into spheres of jurisdiction, except for Cyprus, which had been granted independence by the third Council and remains self-governing to this day.

There are two misunderstandings of this Pentarchy that must be avoided:

the system of patriarchs and metropolitans is based on ecclesiastical structure

the Bishop of Rome (Pope) has supremacy over the other bishops

Regarding the first misunderstanding, the Orthodox do not view the Church from the standpoint of ecclesiastical order, but from the perspective of divine right. They see all bishops as essentially equal, regardless of the prominence of the city which they oversee. They are all divinely appointed teachers of the faith, they all share in Apostolic succession and they all have sacramental powers. If a dispute arises, it is not enough for any one bishop to express his opinion; all diocesan bishops have the right to attend a general council, express their opinion and cast a vote. The system of the Pentarchy does not impair the essential quality of each bishop nor does it strip the local community of the significance Ignatius assigned it.

Regarding the second misunderstanding, the Orthodox do not accept the doctrine of Papal authority as established in 1870 by the Vatican Council and taught in the Roman Catholic Church today. But neither do they deny Rome its place of primacy, as she is first among honor as set up by the second Council. It was Rome, after all, who stayed most true to the faith during many of the heresies over the centuries. Where the Orthodox see Rome going wrong is when they turned this place of 'primacy' in love (as St. Ignatius called it) into a place of supremacy of external jurisdiction and power. And so the primacy assigned to Rome does not overthrow the essential quality of all bishops. The Pope may be the 'first Bishop in the Church,' but he is first among equals.